Reactor and process for preparing hydrogen sulphide

ABSTRACT

The present invention relates to a reactor and to a process for synthesis of hydrogen sulphide from elemental sulphur and hydrogen at elevated pressure and elevated temperature. The invention further relates to the use of the reactor for preparation of hydrogen sulphide in high yield and with a low H 2 S x  content.

The present invention relates to a reactor and to a process forsynthesis of hydrogen sulphide from elemental sulphur and hydrogen atelevated pressure and elevated temperature. The invention furtherrelates to the use of the reactor for preparation of hydrogen sulphidein high yield and with a low H₂S_(x) content.

Hydrogen sulphide is an industrially important intermediate, for examplefor the synthesis of methyl mercaptan, dimethyl sulphide, dimethyldisulphide, sulphonic acids, dimethyl sulphoxide, dimethyl sulphone, andfor numerous sulphidation reactions. It is nowadays obtainedpredominantly from mineral oil and natural gas processing, and byreaction of sulphur and hydrogen.

Hydrogen sulphide is prepared from the elements typically byintroduction of gaseous hydrogen into a sulphur melt, by convertingsulphur to the gas phase and converting it therein in an exothermicreaction with hydrogen to hydrogen sulphide (Ullmann's Encyclopedia ofIndustrial Chemistry, Sixth Edition, 1998, Wiley-VCH).

In order to achieve a satisfactory reaction rate and a high hydrogensulphide yield, the reaction has to take place at elevated temperaturerelative to standard conditions. According to the further use intended,it may be necessary to provide the hydrogen sulphide prepared at apressure of >5 bar. In this case, it would be advantageous to performthe hydrogen sulphide synthesis directly at the pressure required. Thisentails a further temperature increase in order to ensure thatsufficient sulphur is converted to the gas phase. However, theperformance of the hydrogen sulphide synthesis at a temperature of >450°C. has the disadvantage that hydrogen sulphide causes corrosion damageto the reactor material under these conditions. There is accordingly arequirement for a reactor construction which enables high conversionrates and simultaneously avoids damage, at least to the pressure-bearingelements of the reactor.

One approach to enhancing the hydrogen sulphide yield is to increase theresidence time of the hydrogen gas in the sulphur melt. This is done,for example, in U.S. Pat. No. 2,876,070 and DE 10 2008 040 544 A1 by useof reactors having gas collecting regions in the form of intermediatetrays or cups arranged within the sulphur melt. However, this type ofconstruction achieves a conversion of hydrogen of only >96%. Increasingthe number of gas collecting regions could perhaps enhance theconversion, but this would have the disadvantage that a greater reactorvolume would be required.

The principle of increasing the residence time of the hydrogen gas inthe sulphur melt is also accomplished in DE 10 2008 040 544 A1 by areactor having a bed of random ceramic packings in the sulphur melt.This reactor achieves a conversion of >99%. However, this reactor designrequires constant hydrogen supply, since, in the event of a decline orshutdown in the hydrogen supply, the reaction gas can escape completelyfrom the region of the random packing bed, and the random packing bedcan become filled with liquid sulphur. Such a reactor can therefore beoperated only within a very narrow load range.

A further means of enhancing the reaction rate is the use of catalysts,for example oxides or sulphides of cobalt, nickel or molybdenum. Thisapproach is disclosed, for example, in U.S. Pat. No. 2,863,725 and EP 2125 612 B1 in the form of reactors having catalyst-filled tubes whichdip into the sulphur melt, and the gaseous reactants flow through them.However, disadvantages of these reactors are found to be that they areoperated at a pressure of <5 bar, and that, as a result of the fact thatthe reaction of sulphur and hydrogen is predominantly catalytic, a largeamount of catalyst is required.

It is therefore an object of the present invention to provide a reactorfor preparation of hydrogen sulphide from sulphur and hydrogen, whichensures a high hydrogen conversion and a high purity of the hydrogensulphide produced. The reactor should also enable the preparation ofhydrogen sulphide at a pressure of >5 bar, have a very compact designand ensure a very wide load range. Especially in an integratedproduction system, a very wide load range is advantageous, in order tobe able to react flexibly to variations in load, rather than having todispose of excess amounts which are not required by the integratedsystem at that moment but result from inflexibility. Finally, thereactor, from the point of view of costs, maintenance and safety, shouldbe less prone to corrosion damage under the intended operatingconditions. With regard to the energy which is required for provision ofthe sulphur melt and for dissipation of the heat of reaction, aparticularly efficient reactor design is additionally desired. Inaddition, minimization of the amount of catalyst required andmaximization of the catalyst service life is desirable.

To achieve this object, the present invention provides a reactorsuitable for continuous preparation of hydrogen sulphide by exothermicreaction of sulphur and hydrogen to form a final product gas mixtureP_(final) comprising hydrogen sulphide and sulphur at elevatedtemperature and elevated pressure relative to standard conditions, saidreactor comprising

-   -   a lower reactor region suitable for accommodating a sulphur        melt, and    -   one or more non-pressure-bearing first cavern(s) and at least        one supply device suitable for controlled supply of pressurized        gaseous hydrogen per first cavern, said caverns being suitable        for at least temporary accommodation of a product gas mixture P₁        which forms in exothermic reaction and comprises hydrogen        sulphide, sulphur and hydrogen,    -   one or more non-pressure-bearing second cavern(s) which are        arranged above the first cavern(s) and are suitable for at least        temporary accommodation of the product gas mixture P₁ formed in        the first cavern(s) and for formation of further hydrogen        sulphide by exothermic reaction of sulphur and hydrogen to form        a product gas mixture P₂, and    -   a gas collecting region suitable for accommodating the product        gas mixture P_(final) at elevated temperature and elevated        pressure relative to standard conditions.

The reactor is characterized in that at least one of the second cavernshas a greater volume than each of the first caverns, and/or in that atleast one of the second caverns has lower heat removal for constructionreasons than each of the first caverns.

The reactor design according to the invention has the advantage that theresidence time of the hydrogen-containing gas mixture in the one or moresecond caverns is extended, and the heat loss is reduced. This increasesthe hydrogen conversion in the more or more second caverns. Thiscompensates for the decrease in the reaction rate in the second caverns,which is caused by the hydrogen concentration in the second cavernsbeing lower compared to the first caverns.

These measures can achieve the effect that the hydrogen conversion risesto more than 80% or even more than 90% with the second cavern(s). Thehigh hydrogen conversion achieved thereby in the region of the first andsecond caverns particularly avoids the effect that the reaction proceedsin the gas space above the sulphur melt, resulting in overheating of thegas space above the sulphur melt.

The reactor comprises an outer, pressure-bearing vessel. The latterpreferably has the shape of an upright cylinder closed by a hood at eachof the two ends. An inventive reactor has a volume of preferably 0.5 to200 m³. The reactor according to the invention also has one or moresupply devices suitable for supply of liquid sulphur.

The supply devices for introduction of hydrogen are preferably at thelower end of the reactor, such that the gaseous reactants flow throughthe reactor along the longitudinal axis thereof.

The hydrogen introduced into the sulphur melt is saturated with gaseoussulphur and is accommodated by the first cavern(s). In the gas space ofthe first cavern(s), hydrogen and sulphur are reacted in exothermicreaction to hydrogen sulphide, forming the product gas mixture P₁comprising hydrogen, sulphur and hydrogen sulphide. The product gasmixture P₁ leaving the first cavern(s) is at least partiallyaccommodated by the second cavern(s) and reacted there with formation offurther hydrogen sulphide to the product gas mixture P₂. The caverns arepreferably surrounded by the sulphur melt, such that the heat ofreaction released in the caverns is dissipated into the sulphur melt.

The “first cavern” in the context of this invention refers to a cavernif the gas mixture which is collected in the cavern in question has notalready flowed through other caverns beforehand.

A “second cavern” in the context of this invention refers to a cavernwhen at least a portion of the gas mixture which is collected in thecavern in question has flowed through at least one first cavernimmediately beforehand.

A “cavern” in the context of this invention is understood to mean anystructural device that can accommodate and hold a gas volume. A cavernmay take the form, for example, of a hood-shaped installed device underwhich a particular gas volume can collect and flow over the outer edgesof the hood shape, which is open in the downward direction, to higherreactor regions.

In a further illustrative embodiment, a cavern may be formed by beds ofhollow bodies or random packings at different levels. For example, thesehollow bodies or random packings may take the form of beds on screens orscreen boxes. Suitable hollow bodies or random packings are, forexample, straight or curved hollow cylinders, hollow spheres, deformedhollow spheres, bell-shaped bodies, saddle-shaped bodies, screw-shapedbodies or other three-dimensional bodies with indentations and/oropenings. In order to enable the penetration of the gas into thecavities of the hollow bodies or random packings, the hollow bodies andrandom packings preferably have orifices in their outer wall and/or aremanufactured from porous material. A bed of the hollow bodies and randompackings according to the invention preferably has a useful porosity(open porosity) φ_(open) of more than 0.32, more preferably more than0.40, most preferably more than 0.6.

In a preferred embodiment, a cavern consists of a horizontalintermediate tray having one or more orifices through which the gas canflow into higher reactor regions. Along the edges of the orifices, theintermediate tray has weirs running vertically downward, which retain acertain gas volume in the cavern. FIG. 3 shows some illustrativeembodiments of caverns useable in accordance with the invention.

The use of caverns in the form of hood-shaped installed devices or inthe form of the above-described horizontal intermediate trays isgenerally preferable to the use of caverns in the form of beds of hollowbodies or random packings. A disadvantage of hollow bodies or randompackings may be that deposits of reaction by-products may occur overprolonged reactor run time under particular conditions, which couldblock the hollow bodies or random packings. The use of caverns in theform of hood-shaped installed devices or in the form of horizontalintermediate trays is suitable for avoiding this potential disadvantageand may therefore contribute to an extension of the reactor servicelife. Moreover, this cavern design facilitates the adjustment of theresidence time of the gaseous reactants in the caverns, since parameterssuch as the ratio of height to width of the cavern volume, for example,are easier to calculate and to alter.

A further advantage of this cavern design is that the reaction gasitself, in the event of reduced hydrogen supply, does not completelyescape from the caverns, and that a reduction in the hydrogen supplyleads to an extension of the residence time. This residence timeextension is suitable for compensating for a decrease in the reactiontemperature owing to lower hydrogen supply and thus enabling aconstantly high conversion. Caverns in the form of hood-shaped installeddevices or in the form of intermediate trays therefore considerablywiden the acceptable load range of the reactor.

The load range of the reactor may thus be within a range from 0 to 4000m³ (STP) (H₂)/(m³ (cavern volume).h). The cavern volume relates in eachcase to a cavern through which gas flows.

The lower heat removal from a cavern for construction reasons can beachieved, for example, through use of a material with lower thermalconductivity. The cavern in question may either be manufactured fromthis material or at least parts of its surface may be lined with thismaterial. The lining may form a gas slot which additionally reduces heattransfer. Lower heat removal from individual caverns can alternativelyalso be achieved by use of a material with greater material thickness.

If a gas slot is used as an insulator, the cavern may be lined withaluminium or an aluminium alloy in order to increase the corrosionresistance of the cavern material.

In a further preferred embodiment, lower heat removal from individualcaverns is achieved by use of a cavern geometry which hinders heatremoval. For example, heat removal can be reduced by a lower ratio ofcavern surface area to cavern volume.

In a preferred embodiment, the first caverns have a ratio of surface tovolume of 1.5 to 30 m⁻¹, preferably of 3 to 9 m⁻¹, more preferably of 4to 6 m⁻¹, and/or a ratio of height to width of 0.02 to 5, preferably of0.05 to 1, more preferably of 0.08 to 0.12, and/or a ratio of weirlength to throughput of 0.1 to 10 m*h/t_(H2S), preferably of 0.2 to 1.8m*h/t_(H2S), more preferably of 1.0 to 1.2 m*h/t_(H2S). In a furtherpreferred embodiment, at least one of the second caverns has a ratio ofsurface to volume of 1.5 to 30 m⁻¹, preferably of 2.8 to 9 m⁻¹, morepreferably of 3 to 5 m⁻¹, and/or a ratio of height to width of 0.02 to5, preferably of 0.05 to 2, more preferably of 0.1 to 1, and/or a ratioof weir length to throughput of 0.1 to 10 m*h/t_(H2S), preferably of0.15 to 1.8 m*h/t_(H2S), more preferably of 0.2 to 1.1 m*h/t_(H2S).

In a preferred embodiment, the reactor comprises two or more firstcaverns. In this case, the hydrogen supply devices may be designed suchthat the first caverns can be supplied independently with hydrogen. Theamount of sulphur and hydrogen which is fed into an individual caverncan thus be set separately for each first cavern. This enables, forexample, a reduction in hydrogen sulphide production by shutting downthe hydrogen supply to one or more first caverns. The reaction in thefirst cavern(s) remaining may continue at constant hydrogenconcentration and hence under constant reaction conditions.Alternatively, with constant total amount of hydrogen introduced, thehydrogen load can be distributed between several caverns or concentratedin individual caverns in order to influence the reaction conditions inthe first caverns in a controlled manner.

In an alternative embodiment, the supply devices for introduction ofhydrogen are designed such that the hydrogen can be introduced directlyinto the gas space of the first caverns without previously beingsaturated with sulphur. The reactor may be constructed such that it hasseveral supply devices per first cavern, some of which introducehydrogen into the sulphur melt and others introduce hydrogen directlyinto the gas space of the cavern in question. This mode of constructionallows the relative hydrogen concentration, i.e. the ratio of thehydrogen and sulphur reactants, in the first caverns to be controlled.

In a further embodiment, one or more of the second caverns may alsocomprise at least one supply device suitable for controlled supply ofpressurized gaseous hydrogen. In this way, gaseous hydrogen can beintroduced not just into the first caverns but also into the secondcaverns in question, in order, for example, to increase the hydrogenconcentration in P₂ and hence the reaction rate in the second caverns inquestion. The supply devices may—as in the case of the first cavern—beconstructed such that the hydrogen can be introduced either into thesulphur melt below the second caverns or directly into the gas space ofthe second caverns.

The direct introduction of hydrogen into the gas space of a cavern alsohas the consequence that a larger amount of hydrogen and sulphur getsinto the higher caverns.

In particular embodiments, the reactor may additionally comprise one ormore non-pressure-bearing third, and optionally further, correspondinglysuitable caverns arranged above the second cavern(s).

“Third (fourth, fifth, etc.) cavern” in the context of this inventionrefers to a cavern when at least a portion of the gas mixture which iscollected in the cavern in question has flowed through at least onesecond (third, fourth, etc.) cavern immediately beforehand.

In order to enhance the hydrogen conversion in the third and highercaverns, as in the case of the second cavern(s), the residence time ofthe hydrogen-containing gas mixture can be extended or the heat loss ofthe caverns in question minimized. For this purpose, the reactor may bedesigned such that at least one of the third or higher caverns has agreater volume than each of the first caverns, and/or such that at leastone of the third or higher caverns has lower heat removal forconstruction reasons than each of the first caverns. This can beachieved through the above-described construction measures.

During reactor operation, the product gas mixture P_(u) collects abovethe sulphur melt and passes from there through one or morenon-pressure-bearing installed devices into the gas collecting region ofthe reactor. In a preferred embodiment of the reactor, the gascollecting region is arranged above the lower reactor region. Inalternative embodiments the gas collecting region may, for example, alsobe arranged below the lower reactor region, within the lower reactorregion or at the side of the lower reactor region.

In a preferred embodiment, the reactor additionally comprises one ormore non-pressure-bearing installed device(s) suitable for continuoustransfer of the total amount of product gas mixture P_(u) formed in thelower reactor region to the gas collecting region and, in the case thata catalyst is present in the installed device(s), suitable for reactionof sulphur and hydrogen still present in the product gas mixture P_(u)to hydrogen sulphide.

The one or more installed device(s) preferably take the form of U-shapedtubes. The reactor may comprise several identical or similarlyconstructed tubes for transfer of the product gas mixture. The U-shapedtubes are typically arranged horizontally in the reactor, with each ofthe two ends pointing upward. If the gas collecting region is arrangedabove the lower reactor region, the tubes may be connected to anintermediate tray which divides the lower reactor region from the gascollecting region, such that the ends of each of the tubes project intothe gas collecting region, while the U-shaped parts of the tubes arewithin the lower reactor region. The limbs of the individual tubes mayalso be of different lengths, such that the ends of the shorter legs arewithin the lower reactor region and the ends of the longer legs projectinto the gas collecting region.

In an alternative embodiment of the reactor, the one or more installeddevice(s) take the form of straight, vertical tubes. The straight tubesare preferably arranged such that they, if the lower reactor regioncontains a sulphur melt, dip into the sulphur melt and connect the gasspace above the sulphur melt to the gas collecting region arrangedwithin or below the lower reactor region.

The tubes preferably have a diameter of 20 to 3000 mm, preferably of 60to 150 mm, more preferably of 80 to 120 mm. Through orifices which maybe provided, for example, in the side wall of a tube or, in the case ofU-shaped tubes with limbs of unequal length, at the end of the shorterlimb, the product gas mixture P_(u) passes from the lower reactor regioninto the tubes. The orifices are preferably arranged at a distance of0.1 to 3 m, preferably of 0.4 to 1.4 m, above the phase boundary of thesulphur melt, in order to prevent introduction of liquid sulphur intothe tubes. The product gas mixture flows along the tubes and passesthrough orifices mounted, for example, at the end of the tubes into thegas collecting region.

The one or more installed device(s) preferably contain a heterogeneouscatalyst for further conversion of hydrogen and sulphur present in theproduct gas P_(u) to hydrogen sulphide. Typically, a cobalt- andmolybdenum-containing catalyst is used. This is preferably asulphur-resistant hydrogenation catalyst which preferably consists of asupport, for example silica, alumina, zirconia or titania, and comprisesone or more of the active metals molybdenum, nickel, tungsten, iron,vanadium, cobalt, sulphur, selenium, phosphorus, arsenic, antimony andbismuth. Particular preference is given to a mixed compound composed ofCoO, MoO₃, Al₂O₃ with or without sulphate in tablet form. The catalystis preferably positioned in the form of a fixed bed. In that case, theheterogeneous catalyst takes the form of pellets, tablets or comparableshaped bodies. However, other designs are also possible, for examplehoneycombs or a fluidized bed. The catalyst may likewise be present inthe installed devices as a coating on random packings, monoliths orknits.

The amount of catalyst positioned in the installed devices is guided bythe amount of residual hydrogen to be converted, the dimensions of theinstalled devices, the type of catalyst and possibly further factors. Inthe case of a catalyst bed, the amount of catalyst used, depending onthe amount of hydrogen supplied, should be such that the hydrogen loaddoes not exceed a value of 4000 m³ (STP) (H₂)/(m³ (catalyst bedvolume)·h).

In addition, further catalysts may be provided at one or more sites inthe reaction vessel. In this case, the catalyst is preferably positionedsuch that it does not come into contact with the liquid sulphur. Thiscatalyst may be in the form of pellet beds, of suspended powder in theliquid sulphur, or of a coating on random packings, monoliths or knits.If further catalyst is used, this catalyst may be provided in theinternals acting as caverns. In a further embodiment, this catalyst maybe provided above the liquid sulphur and all caverns.

In a preferred embodiment of the invention, one, more than or all of theinstalled devices for transfer of the product gas mixture P_(u) from thelower reactor region to the gas collecting region are arranged in termsof construction such that, after sufficient filling of the lower reactorregion with a sulphur melt, they are in thermal contact with the sulphurmelt such that, if the installed device contains a catalyst, thecatalyst is cooled by transfer of heat to the sulphur melt. In the caseof the above-described U-shaped or straight tubes, these are preferablydesigned such that the outer shell area, in the region of the tubefilled with catalyst, is surrounded by the sulphur melt to an extent ofmore than 20%, preferably to an extent of more than 50%, more preferablyto an extent of more than 75%.

In order to ensure substantially homogeneous temperature distributionwithin the reactor, the reactor preferably comprises an inner wallwhich, in the course of operation of the reactor, with involvement ofthe space between outer reactor wall and the inner wall, allowscontinuous circulation of the sulphur melt according to the airlift pumpprinciple. Sulphur flows here, driven by the introduction of hydrogenfrom the base, upward within the reactor region surrounded by the innerwall, and flows to the base within the space between outer reactor walland the inner wall. The sulphur flowing downward can be cooled byremoval of heat via the outer reactor wall. In a preferred embodiment,the cooling of the sulphur flowing downward is supported by heatexchangers provided, for example, on the outer reactor wall or in thespace between outer reactor wall and inner wall.

In a preferred embodiment, the reactor comprises a reflux condensersuitable for condensation of the sulphur present in the product gasmixture P_(final). The reflux condenser is preferably arranged above thegas collecting region. The reflux condenser is connected to the gascollecting region via an input line suitable for transport of theproduct gas mixture P_(final) from the gas collecting region to thereflux condenser, and has a return line suitable for return of thecondensed sulphur to the reactor, preferably to the lower reactorregion. The return of the condensed sulphur also serves to cool thesulphur melt and thus contributes to maintenance of a constanttemperature of the sulphur melt.

Even in the course of long operation for several years or decades, thereactor according to the invention has to be maintained or repaired onlyinfrequently. The construction according to the invention avoids theoccurrence of excess temperatures in pressure-bearing parts and thusincreases plant safety, because reduced corrosion in this regionminimizes the risk of material failure and the probability of accidentsresulting from the escape of hazardous substances, for example hydrogensulphide. The low inspection, maintenance and repair demands lower thecosts and improve availability.

The present invention also provides a process for preparing hydrogensulphide by exothermic reaction of sulphur with hydrogen at elevatedtemperature and elevated pressure relative to standard conditions toform a product gas mixture P_(final) comprising hydrogen sulphide andsulphur, said process comprising the following steps:

-   -   providing a sulphur melt in a lower reactor region of a        pressurized reactor,    -   supplying pressurized hydrogen into the sulphur melt, the        hydrogen supplied being accommodated at least partly, together        with sulphur converted from the sulphur melt to the gaseous        state, by at least one non-pressure-bearing first cavern,    -   at least temporarily leaving the hydrogen and the sulphur in the        first cavern(s), so as to form, in exothermic reaction, a        product gas mixture P₁ comprising hydrogen sulphide, sulphur and        hydrogen,    -   accommodating the product gas mixture P₁ in one or more second        cavern(s) and at least temporarily leaving the product gas        mixture P₁ therein, such that the sulphur and hydrogen present        in the product gas mixture P₁ are reacted with formation of        further hydrogen sulphide to a product gas mixture P₂, and use        of at least one second cavern having a greater volume than each        of the one or more first caverns and/or a lower heat removal for        construction reasons than each of the one or more first caverns        results in an increase in the hydrogen conversion in the second        cavern in question, and    -   collecting the product gas mixture P_(final) in a gas collecting        region.

The process is preferably performed in the reactor according to theinvention already described.

Rather than pure hydrogen, it is also possible to pass contaminatedhydrogen through the sulphur melt. The impurities may, for example, becarbon dioxide, hydrogen sulphide, water, methanol, methane, ethane,propane or other volatile hydrocarbons. Preference is given to usinghydrogen having a purity greater than 65% based on the gas volume. Theimpurities in the hydrogen or reaction products thereof are preferablynot removed before the synthesis of methyl mercaptan, but left in thereactant mixture. The sulphur used may also contain differentimpurities.

The pressure and volume of the hydrogen supplied are guided by thepressure at which the reactor is operated and the volume of hydrogenrequired. The amount of sulphur used is virtually stoichiometric to theamount of hydrogen used. Spent sulphur is replenished during theprocess.

In a further embodiment of the process, at least a portion of thehydrogen supplied into the sulphur melt is accommodated directly by atleast one of the second caverns. “Directly” is understood here to meanthat the hydrogen supplied is not accommodated by a first cavern beforepassing into a second cavern. The hydrogen supply can thus be controlledwith the purpose of influencing the reaction rate in the first andsecond caverns in different ways.

The process can be performed in such a way that the product gas mixtureis accommodated and left at least temporarily in at least one third orhigher cavern, so as to react the sulphur and hydrogen present in theproduct gas mixture P₂ with formation of further hydrogen sulphide.

In an alternative embodiment of the process, at least some of thehydrogen is supplied at least to the first and/or higher caverns suchthat it does not come into contact with the sulphur melt beforehand.This can increase the hydrogen concentration in the caverns in questionwithout also simultaneously transferring additional sulphur to the gasspace of the cavern.

The supply of hydrogen into the liquid sulphur below a cavern (forexample a second cavern) firstly has the effect that the hydrogensupplied to this cavern is increased, and secondly that sulphur is alsotransferred from the liquid sulphur to the gas space of this cavern.

In one embodiment of the process, the total amount of the product gasmixture P_(u) formed in the lower reactor region is continuouslytransferred to the gas collecting region by means of one or morenon-pressure-bearing installed device(s), wherein by use of a catalystin the installed device(s) the sulphur and hydrogen present in theproduct gas mixture P_(u) are reacted with formation of further hydrogensulphide.

The process is preferably performed such that the heat of reactionreleased by the reaction of sulphur and hydrogen is released into thesulphur melt as completely as possible. This includes the heat ofreaction released over the catalyst.

Preferably, heat transfer of the heat of reaction, released by thereaction of sulphur and hydrogen in the catalyst, to the sulphur meltthus cools the catalyst.

The process is preferably performed in such a way that the proportion ofhydrogen sulphide in the product gas mixture P_(u) prior to introductioninto the installed device containing the catalyst is at least 60%,preferably at least 90%, of the gas volume. The process conditionsrequired for this purpose are described below. This has the advantagethat the low proportion of hydrogen in the region of the catalystprevents overheating of the catalyst and thus increases the service lifeof the catalyst.

The process preferably comprises an additional process step in which thesulphur present in the product gas mixture P_(final) is condensed andrecycled directly into the reactor, preferably to the lower reactorregion. As a result there is the advantageous effect that cooling of thesulphur melt takes place as a function of the amount of hydrogensulphide produced. More particularly, at the moment at which thetemperature of the sulphur melt rises, there is likewise an increase inthe hydrogen conversion, sulphur vaporization and sulphur reflux, suchthat overheating of the sulphur melt is counteracted. The sulphurcondensation is preferably effected at a temperature of 120 to 150° C.

The process according to the invention can typically be performed at apressure of 1 to 30 bar, preferably at 5 to 15 bar, more preferably 7 to12 bar. The temperature of the sulphur melt is typically 300 to 600° C.,preferably 380 to 480° C., more preferably 400 to 450° C. Hydrogenconversions of 99.9% are thus easily achievable. Hydrogen conversions inthe region of 99.93% have likewise been observed.

The process according to the invention enables the production ofhydrogen sulphide having a purity of more than 99.8% by volume. A purityof up to 99.85% by volume has likewise been found. In this case, theproduct gas mixture, after condensation of sulphur present, may containbetween 0.05 and 0.15% by volume of hydrogen, 10 to 30 ppm of sulphurand 400 to 600 ppm of sulphanes. Sulphanes in the context of thisinvention refer to hydrogen polysulphides according to the empiricalformula H₂S_(x) where x is typically an integer from 2 to 10. Theabovementioned sulphur concentrations are already enabled by sulphurcondensation within the abovementioned temperature range. Freezing attemperatures below 120° C.—as known from other H₂S processes—is notrequired for this purpose.

The present invention also relates to the use of a reactor according tothe invention for preparation of hydrogen sulphide having a sulphanecontent not exceeding 600 ppm, preferably not exceeding 400 ppm, morepreferably not exceeding 200 ppm.

The present invention is further described by the following examples:

1. Reactor (1) suitable for continuous preparation of hydrogen sulphideby exothermic reaction of sulphur and hydrogen to form a final productgas mixture P_(final) comprising hydrogen sulphide and sulphur atelevated temperature and elevated pressure relative to standardconditions, said reactor (1) comprising

-   -   a lower reactor region (2) suitable for accommodating a sulphur        melt (3),    -   one or more non-pressure-bearing first cavern(s) (4) and at        least one supply device (5, 5 a) suitable for controlled supply        of pressurized gaseous hydrogen per first cavern, said caverns        (4) being suitable for at least temporary accommodation of a        product gas mixture P₁ which forms in exothermic reaction and        comprises hydrogen sulphide, sulphur and hydrogen,    -   one or more non-pressure bearing second cavern(s) (8) which are        arranged above the first cavern(s) (4) and are suitable for at        least temporary accommodation of the product gas mixture P₁        formed in the first cavern(s) (4) and for formation of further        hydrogen sulphide by exothermic reaction of sulphur and hydrogen        to form a product gas mixture P₂, and    -   a gas collecting region (6) suitable for accommodating the        product gas mixture P_(final) at elevated temperature and        elevated pressure relative to standard conditions,

characterized in that at least one of the second caverns (8, 10) has agreater volume than each of the first caverns (4), and/or in that atleast one of the second caverns (8, 10) has lower heat removal forconstruction reasons than each of the first caverns (4).

2. Reactor according to Example 1, characterized in that the reactor (1)comprises at least two non-pressure-bearing first caverns (4) and atleast one supply device (5, 5 a) suitable for controlled supply ofpressurized gaseous hydrogen per first cavern (4), said first caverns(4) being suitable for at least temporary accommodation of the productgas mixture P₁ which forms.

3. Reactor according to Example 1 or 2, characterized in that at leastone of the second caverns (8) comprises at least one supply device (9, 9a) suitable for controlled supply of pressurized gaseous hydrogen.

4. Reactor according to any one of Examples 1 to 3, characterized inthat the reactor (1) additionally comprises one or morenon-pressure-bearing third (10), and optionally further, correspondinglysuitable caverns arranged above the second cavern(s) (8).

5. Reactor according to Example 4, characterized in that at least one ofthe third or higher caverns (10) has a greater volume than each of thefirst caverns (4), and/or in that at least one of the third or highercaverns (8, 10) has lower heat removal for construction reasons thaneach of the first caverns (4).

6. Reactor according to any one of Examples 1 to 5, characterized inthat the reactor (1) additionally comprises one or morenon-pressure-bearing installed device(s) (7) suitable for continuoustransfer of the total amount of product gas mixture P_(u) formed in thelower reactor region (2) to the gas collecting region (6) and, in thecase that a catalyst is present in the installed device(s) (7), suitablefor reaction of sulphur and hydrogen still present in the product gasmixture P_(u) to hydrogen sulphide.

7. Reactor according to Example 6, characterized in that one, more thanone or all of the installed devices (7) for transfer of the product gasmixture P, from the lower reactor region (2) to the gas collectingregion (6) are arranged in terms of construction such that, aftersufficient filling of the lower reactor region (2) with a sulphur melt(3), they are in thermal contact with the sulphur melt (3) such that, ifthe installed device (7) contains a catalyst, the catalyst is cooled bytransfer of heat to the sulphur melt (3).

8. Reactor according to any one of Examples 1 to 7, characterized inthat the reactor comprises an inner wall (11) which, in the course ofoperation of the reactor with involvement of the space between outerreactor wall and the inner wall (11), allows continuous circulation ofthe sulphur melt according to the airlift pump principle.

9. Reactor according to any one of Examples 1 to 8, characterized inthat the reactor additionally comprises

-   -   a reflux condenser suitable for condensation of the sulphur        present in the product gas mixture P_(final),    -   an input line suitable for transport of the product gas mixture        P_(final) from the gas collecting region to the reflux condenser        and    -   a return line suitable for return of the condensed sulphur to        the reactor.

10. Process for preparing hydrogen sulphide by exothermic reaction ofsulphur with hydrogen at elevated temperature and elevated pressurerelative to standard conditions to form a product gas mixture P_(final)comprising hydrogen sulphide and sulphur, said process comprising thefollowing steps:

-   -   providing a sulphur melt in a lower reactor region of a        pressurized reactor,    -   supplying pressurized hydrogen into the sulphur melt, the        hydrogen supplied being accommodated at least partly, together        with sulphur converted from the sulphur melt to the gaseous        state, by at least one non-pressure-bearing first cavern,    -   at least temporarily leaving the hydrogen and the sulphur in the        first cavern(s), so as to form, in exothermic reaction, a        product gas mixture P₁ comprising hydrogen sulphide, sulphur and        hydrogen,    -   accommodating the product gas mixture P₁ in one or more second        cavern(s) and at least temporarily leaving the product gas        mixture P₁ therein, such that the sulphur and hydrogen present        in the product gas mixture P₁ are reacted with formation of        further hydrogen sulphide to a product gas mixture P₂, and use        of at least one second cavern having a greater volume than each        of the one or more first caverns and/or a lower heat removal for        construction reasons than each of the one or more first caverns        results in an increase in the hydrogen conversion in the second        cavern in question, and    -   collecting the product gas mixture P_(final) in a gas collecting        region.

11. Process according to Example 10, characterized in that at least aportion of the hydrogen supplied into the sulphur melt is accommodateddirectly by one or more second cavern(s).

12. Process according to Example 10 or 11, characterized in that theproduct gas mixture is accommodated and left at least temporarily in oneor more third or higher cavern(s), so as to react the sulphur andhydrogen present in the product gas mixture P₂ with formation of furtherhydrogen sulphide.

13. Process according to any one of Examples 10 to 12, characterized inthat the total amount of the product gas mixture P_(u) formed in thelower reactor region is continuously transferred to the gas collectingregion by means of one or more non-pressure-bearing installed device(s),wherein by use of a catalyst in the installed device(s) sulphur andhydrogen present in the product gas mixture P_(u) are reacted withformation of further hydrogen sulphide.

14. Process according to Example 13, characterized in that the catalystis cooled by heat transfer of the heat of reaction, released by thereaction of sulphur and hydrogen in the catalyst, to the sulphur melt.

15. Process according to Example 13 or 14, characterized in that theproportion of hydrogen sulphide in the product gas mixture P_(u) priorto introduction into the installed device(s) containing the catalyst isat least 60% of the gas volume.

16. Process according to any one of Examples 10 to 15, characterized inthat it comprises an additional process step in which the sulphurpresent in the product gas mixture P_(final) is condensed and recycleddirectly into the reactor.

17. Process according to any one of Examples 10 to 16, characterized inthat the preparation of hydrogen sulphide is performed at a pressure of5 to 15 bar.

18. Process according to any one of Examples 10 to 17, characterized inthat the temperature of the sulphur melt is 400 to 450° C.

19. Process according to any one of Examples 10 to 18, characterized inthat the sulphur melt is circulated continuously according to theairlift pump principle.

20. Use of a reactor according to any one of Examples 1 to 9 forpreparation of hydrogen sulphide having a sulphane content not exceeding600 ppm.

FIG. 1 shows, by way of example and schematically, a reactor which canbe used in accordance with the invention for preparation of hydrogensulphide from hydrogen and sulphur.

The reactor 1, shown in FIG. 1, comprises an outer, pressure-bearingvessel containing a sulphur melt 3 in the lower region 2 thereof. Bymeans of supply devices 5, hydrogen can be introduced into the sulphurmelt, and is accommodated directly by the first caverns 4. Supplydevices 5 a can also be used to introduce hydrogen directly into the gasspace 12 of the first caverns 4. In the gas space 12 of the firstcaverns 4, the product gas mixture P₁ comprising hydrogen, sulphur andhydrogen sulphide is formed. The reactor shown also has additionalsupply devices 9, by means of which hydrogen can be supplied directly tothe second caverns 8, wherein the product gas mixture P₂ forms in thegas space 13. By means of supply devices 9 a, hydrogen can also beintroduced directly into the gas space 13 of the second caverns 8. Thegas mixture flowing upward is temporarily accommodated by the thirdcaverns 10, wherein the product gas mixture P₃ forms in the gas space14. In the gas space 15, the entire product gas mixture P_(u) formed inthe lower reactor region collects. The gas space 15 is separated fromthe gas collecting region 6 by an intermediate tray 16. The product gasmixture P_(u) is transferred from the gas space 15 to the gas collectingregion 6 using the installed device 7. The installed device 7 isdesigned as a U-shaped tube which dips into the sulphur melt 3. Viaorifices 17 and 18, gas can flow into and out of the installed device 7.The installed device 7 can accommodate a catalyst which enables thefurther conversion of sulphur and hydrogen in the product gas mixtureP_(u) to form the product gas mixture P_(final). The product gas mixtureP_(final) comprising sulphur and hydrogen sulphide is accommodated inthe gas collecting region 6 and can be withdrawn from the reactor viathe orifice 19, or optionally supplied to a reflux condenser. In theregion of the sulphur melt, the reactor also comprises an inner wall 11which serves for continuous circulation of the sulphur melt by theairlift pump principle.

FIG. 2 shows a schematic of four different illustrative cavernarrangements in the case of a reactor with first, second and thirdcaverns. The caverns consist of intermediate trays each having oneorifice. The orifices are each arranged such that the gas mixture mustflow from the first to the second and from the second to the thirdcavern. Top left is a reactor according to the invention with a first,second and third cavern in each case. The three caverns each have thesame geometry. Top right is a reactor according to the invention with afirst, second and third cavern in each case, with continuouslyincreasing weir height and hence increasing residence time of the gasmixture from the first to the third cavern. Bottom left is a reactoraccording to the invention with a first, second and third cavern in eachcase, all caverns having the same weir height. The second cavern has acircular orifice in the middle of the intermediate tray. Bottom right isa reactor according to the invention with a first, second and thirdcavern in each case, with continuously increasing weir height and henceincreasing residence time of the gas mixture from the first to the thirdcavern.

FIG. 3 shows a schematic of illustrative embodiments of caverns. Thecaverns shown have an intermediate tray with a weir running along theedge thereof. Various embodiments are shown for the lower edge of theweir A and the profile of the weir B.

EXAMPLES Example 1 (Comparative Example)

1000 I (STP)/h of hydrogen were introduced continuously via a frit atthe base into a tube having an internal diameter of 5 cm which had beenfilled with liquid sulphur up to a height of 1 m. The consumption ofsulphur was compensated for by further metered addition of liquidsulphur, while keeping the fill level constant. Sulphur removed from theproduct gas stream by condensation was recycled into the upper region ofthe tube in liquid form. Above the liquid sulphur, jacketedthermocouples for temperature measurement were provided at intervals of10 cm. While the reactor was heated to 400° C. electrically via theouter wall, a homogeneous temperature of about 397° C. was presentwithin the sulphur. However, the thermocouples above the sulphur showeda maximum temperature of 520° C. In addition, above the liquid sulphur,new material samples made from standard stainless steel (1.4571) wereprovided at the location of maximum temperature. After an operating timeof about 400 h, the material samples were removed and showed severecorrosion phenomena in the form of flaking and weight loss.

Example 2 (Comparative Example)

Example 1 was repeated, except that the height of the liquid sulphur wasraised to 4 m. The value of the maximum temperature above the liquidsulphur was maintained. Severe corrosion phenomena likewise occurred onthe material samples.

Example 3 (Comparative Example)

Example 2 was repeated, except that 15% by weight of a pulverulentCo₃O₄MoO₃/Al₂O₃ catalyst were suspended in liquid sulphur. The value ofthe maximum temperature above the liquid sulphur was maintained. Severecorrosion phenomena likewise occurred on the material samples.

Example 4

The process according to the invention was examined in a pilot plant.The pilot reactor had a height of approx. 5.5 m, a diameter of approx.0.5 m and a volume of approx. 0.8 m³. The pilot plant was equipped withfour caverns of equal dimensions in series. 70 m³ (STP)/h of hydrogenwere metered in continuously via the hydrogen feeds, which correspondedto a hydrogen load of 3700 m³ (STP)(H₂)/(m³ (cavern volume)·h) based onthe single cavern. Spent sulphur was replenished under fill levelcontrol. Sulphur removed from the product gas stream by condensation wasrecycled into the reactor in liquid form. The pressure in the reactorwas 12 bar. The temperature in the liquid sulphur was 430° C. Theresidence time in the caverns was 5 s in each case. The H₂ conversionthrough homogeneous reaction in the caverns was about 90%. By means ofthermocouples installed in a fixed manner in the reactor, thetemperature within the caverns and above the sulphur melt was measured.The highest temperature measured in the caverns under thesecircumstances was 479° C. Above the liquid sulphur phase, nocommencement of a homogeneous reaction was discernible. The gastemperature above the liquid sulphur corresponded virtually to thetemperature of the liquid sulphur, such that there were no increaseddemands on the material of the pressure-bearing jacket in the region ofthe gas phase above the liquid sulphur.

The gas phase then flowed to and through the catalyst in the installeddevice, as shown schematically in FIG. 1 (7). The hydrogen remaining wasthen converted virtually completely over the catalyst (overallconversion of H₂: 99.86 mol %). The gas hourly space velocity on thecatalyst was 3700 m³ (STP)(H₂)/(m³ (bed volume of catalyst)·h). Therewas virtually no occurrence of corrosion in the form of flaking orweight loss on the material used. Material samples made from standardstainless steel (1.4571) which were installed for comparative purposeshad only moderate corrosion attack.

LIST OF REFERENCE NUMERALS

(1) Reactor

(2) Lower reactor region

(3) Sulphur melt

(4) First caverns

(5, 5 a) Hydrogen supply device to the first caverns

(6) Gas collecting region

(7) Installed device for transfer of gas from the lower reactor regionto the gas collecting region, optionally containing a catalyst

(8) Second caverns

(9, 9 a) Hydrogen supply device to the second caverns

(10) Third caverns

(11) Inner wall

(12) Gas space of the first caverns

(13) Gas space of the second caverns

(14) Gas space of the third caverns

(15) Gas space of the lower reactor region

(16) Intermediate tray

(17) Orifice

(18) Orifice

(19) Orifice

1. A reactor comprising: a lower reactor region suitable for accommodating a sulfur melt, a non-pressure-bearing first cavern and a supply device suitable for controlled supply of pressurized gaseous hydrogen per first cavern, wherein the first cavern is suitable for at least temporary accommodation of a product gas mixture P₁ which forms in exothermic reaction and comprises hydrogen sulfide, sulfur and hydrogen, a non-pressure bearing second cavern arranged above the first cavern and suitable for at least temporary accommodation of the product gas mixture P₁ formed in the first cavern and for formation of further hydrogen sulfide by exothermic reaction of sulfur and hydrogen to form a product gas mixture P₂, and a gas collecting region suitable for accommodating the product gas mixture P_(final) at elevated temperature and elevated pressure relative to standard conditions, wherein at least one of the second caverns has lower heat removal than each of the first caverns (4), and wherein the reactor is suitable for continuous preparation of hydrogen sulfide by exothermic reaction of sulfur and hydrogen to form a final product gas mixture P_(final) comprising hydrogen sulfide and sulfur at elevated temperature and elevated pressure relative to standard conditions.
 2. The reactor of claim 1, comprising at least two non-pressure-bearing first caverns and at least one supply device suitable for controlled supply of pressurized gaseous hydrogen per first cavern, wherein the first caverns are suitable for at least temporary accommodation of the product gas mixture P₁ which forms.
 3. The reactor of claim 1, wherein at least one of the second caverns comprises a supply device suitable for controlled supply of pressurized gaseous hydrogen.
 4. The reactor of claim 1, further comprising a non-pressure-bearing third, and optionally further, correspondingly suitable caverns arranged above the second cavern.
 5. The reactor of claim 4, wherein (i) at least one of the third or higher caverns has a greater volume than each of the first caverns, (ii) at least one of the third or higher caverns has lower heat removal for construction reasons than each of the first caverns, or both (i) and (ii).
 6. The reactor of claim 1, further comprising a non-pressure-bearing installed device suitable for continuous transfer of the total amount of product gas mixture P_(u) formed in the lower reactor region to the gas collecting region and, in the case that a catalyst is present in the installed device, suitable for reaction of sulfur and hydrogen still present in the product gas mixture P_(u) to hydrogen sulfide.
 7. The reactor of claim 6, wherein at least one of the installed devices for transfer of the product gas mixture P_(u) from the lower reactor region to the gas collecting region are arranged in terms of construction such that, after sufficient filling of the lower reactor region with a sulfur melt, they are in thermal contact with the sulfur melt such that, if the installed device contains a catalyst, the catalyst is cooled by transfer of heat to the sulfur melt.
 8. The reactor of claim 1, further comprising an inner wall which, in the course of operation of the reactor with involvement of the space between an outer reactor wall and the inner wall, allows continuous circulation of the sulfur melt according to an airlift pump principle.
 9. The reactor of claim 1, further comprising: a reflux condenser suitable for condensation of the sulfur present in the product gas mixture P_(final), an input line suitable for transport of the product gas mixture P_(final) from the gas collecting region to the reflux condenser and a return line suitable for return of the condensed sulfur to the reactor.
 10. A process for preparing hydrogen sulfide by exothermic reaction of sulphur with hydrogen at elevated temperature and elevated pressure relative to standard conditions to form a product gas mixture P_(final) comprising hydrogen sulfide and sulfur, the process comprising: supplying pressurized hydrogen into a sulfur melt, the hydrogen supplied being accommodated at least partly, together with sulfur converted from the sulfur melt to the gaseous state, by at least one non-pressure-bearing first cavern, at least temporarily leaving the hydrogen and the sulfur in the first cavern, so as to form, in exothermic reaction, a product gas mixture P₁ comprising hydrogen sulfide, sulfur and hydrogen, accommodating the product gas mixture P₁ in one or more second cavern(s) and at least temporarily leaving the product gas mixture P₁ therein, such that the sulfur and hydrogen present in the product gas mixture P₁ are reacted with formation of further hydrogen sulfide to a product gas mixture P₂, and use of at least one second cavern having a lower heat removal than each of the one or more first caverns results in an increase in the hydrogen conversion in the second cavern in question, and collecting the product gas mixture P_(final) in a gas collecting region.
 11. The process of claim 10, wherein at least a portion of the hydrogen supplied into the sulfur melt is accommodated directly by one or more of the second cavern(s).
 12. Process according to claim 10, characterized in that The process of claim 10, wherein the product gas mixture is accommodated and left at least temporarily in one or more third or higher cavern(s), so as to react the sulfur and hydrogen present in the product gas mixture P₂ with formation of further hydrogen sulfide.
 13. The process of claim 10, wherein a total amount of the product gas mixture P_(u) formed in the lower reactor region is continuously transferred to the gas collecting region by one or more non-pressure-bearing installed device(s), wherein by use of a catalyst in the installed device(s) sulfur and hydrogen present in the product gas mixture P_(u) are reacted with formation of further hydrogen sulfide.
 14. The process of claim 13, wherein the catalyst is cooled by heat transfer of the heat of reaction, released by the reaction of sulfur and hydrogen in the catalyst, to the sulfur melt.
 15. The process of claim 13, wherein the proportion of hydrogen sulfide in the product gas mixture P_(u) prior to introduction into the installed device(s) containing the catalyst is at least 60% of the gas volume.
 16. The process of claim 10, further comprising condensing and recycling the sulfur present in the product gas mixture P_(final) directly into the reactor.
 17. The process of claim 10, wherein the preparation of hydrogen sulfide is performed at a pressure of 5 to 15 bar.
 18. The process of claim 10, wherein the temperature of the sulfur melt is 400 to 450° C.
 19. The process of claim 10, wherein the sulfur melt is circulated continuously according to an airlift pump principle.
 20. A process for preparation of hydrogen sulfide having a sulfane content not exceeding 600 ppm, the process comprising preparing the hydrogen sulfide in the reactor of claim
 1. 